A low-light colonoscopy video enhancement method is needed as poor illumination in colonoscopy can hinder accurate disease diagnosis and adversely affect surgical procedures. Existing low-light video enhancement methods usually apply a frame-by-frame enhancement strategy without considering the temporal correlation between them, which often causes a flickering problem. In addition, most methods are designed for endoscopic devices with fixed imaging styles and cannot be easily adapted to different devices. In this paper, we propose a Style-Guided Network (SGNet) for unpaired Low-Light Colonoscopy Video Enhancement (LLCVE). Given that collecting content-consistent paired videos is difficult, SGNet adopts a CycleGAN-based framework to convert low-light videos to normal-light videos, in which a Temporal Compensation (TC) module and a Style Guidance (SG) module are proposed to alleviate the flickering problem and achieve flexible style transfer, respectively. The TC module compensates for a low-light frame by learning the correlated feature of its adjacent frames, thereby improving the temporal smoothness of the enhanced video. The SG module encodes the text of the imaging style and adaptively explores its intrinsic relationships with video features to obtain style representations, which are then used to guide the subsequent enhancement process. Extensive experiments on a curated database show that SGNet achieves promising performance on the LLCVE task, outperforming state-of-the-art methods in both quantitative metrics and visual quality.

Captured colonoscopy videos usually suffer from multiple real-world distortions, such as motion blur, low brightness, abnormal exposure, and object occlusion, which impede visual interpretation. However, existing works mainly investigate the impacts of synthesized distortions, which differ from real-world distortions greatly. This research aims to carry out an in-depth study for colonoscopy Video Quality Assessment (VQA). In this study, we advance this topic by establishing both subjective and objective solutions. Firstly, we collect 1,000 colonoscopy videos with typical visual quality degradation conditions in practice and construct a multi-attribute VQA database. The quality of each video is annotated by subjective experiments from five distortion attributes (i.e., temporal-spatial visibility, brightness, specular reflection, stability, and utility), as well as an overall perspective. Secondly, we propose a Distortion Attribute Reasoning Network (DARNet) for automatic VQA. DARNet includes two streams to extract features related to spatial and temporal distortions, respectively. It adaptively aggregates the attribute-related features through a multi-attribute association module to predict the quality score of each distortion attribute. Motivated by the observation that the rating behaviors for all attributes are different, a behavior guided reasoning module is further used to fuse the attribute-aware features, resulting in the overall quality. Experimental results on the constructed database show that our DARNet correlates well with subjective ratings and is superior to nine state-of-the-art methods.

In recent years, there has been significant progress in polyp segmentation in white-light imaging (WLI) colonoscopy images, particularly with methods based on deep learning (DL). However, little attention has been paid to the reliability of these methods in narrow-band imaging (NBI) data. NBI improves visibility of blood vessels and helps physicians observe complex polyps more easily than WLI, but NBI images often include polyps with small/flat appearances, background interference, and camouflage properties, making polyp segmentation a challenging task. This paper proposes a new polyp segmentation dataset (PS-NBI2K) consisting of 2,000 NBI colonoscopy images with pixel-wise annotations, and presents benchmarking results and analyses for 24 recently reported DL-based polyp segmentation methods on PS-NBI2K. The results show that existing methods struggle to locate polyps with smaller sizes and stronger interference, and that extracting both local and global features improves performance. There is also a trade-off between effectiveness and efficiency, and most methods cannot achieve the best results in both areas simultaneously. This work highlights potential directions for designing DL-based polyp segmentation methods in NBI colonoscopy images, and the release of PS-NBI2K aims to drive further development in this field.